In a communication network, source-based routing provide a system and method for computing paths to be taken for connection requests as they route through nodes in the network. Typically in a source-routing protocol the source node computes an optimum path that a certain connection request should take throughout the network to reach its destination to reach its destination. The path is computed based on the source node's view of the network topology and the connection request requirements (e.g. bandwidth, class of service, etc.). The computation is performed such that the resulting path satisfies and complies to the connection request requirements. Once the full path is computed, it is included in the connection request's signaled message and the connection request is launched through the network, traversing the nodes that are indicated in the computed path. Each node, that receives the connection request, strictly follows the signaled path, and forwards the connection request to the next node as indicated in the given path. This is contrasted against a hop-by-hop protocol, where the next link that is chosen is decided by each successive node in the dynamically selected path. It will be appreciated that the terms “call” and “connection request” in this environment may be used interchangeably, although the term “connection request” has a more generic meaning, as it can also relate to ATM, IP and other connections for different network architectures.
Further, policy routing is utilized in the art of communications networks in order to control the manner in which network traffic or its related network connections are routed across a routing domain of the network. As such, paths can be assigned to have specific bandwidth and quality of service (QoS) parameters.
In an ATM network, the ATM Forum's Private Network-to-Network Interface (PNNI) provides a source-routing protocol for ATM transmissions. As a routing protocol, PNNI allows switches in the network to determine the best route to establish a connection.
One known routing and signaling specification for the support of policy routing is that provided by the specification of The ATM Forum Technical Committee entitled “Policy Routing”, version 1.0, which is dated April 2003 and is identified as document number af-cs-0195.000 (the “Policy Routing Specification”), the contents of which are hereby incorporated by reference. The Policy Routing Specification is an addendum to existing signaling specifications of The ATM Forum Technical Committee, namely: “ATM User-Network Interface (UNI) Signaling Specification”, version 4.1, which is dated April 2002 and is identified as document number af-sig-0061.002; “ATM Inter-Network Interface Specification”, version 1.1, which is dated September 2002 and is identified as document number af-cs-0125.002; and “Private Network-Network Interface Specification, version 1.1, which is dated April 2002 and is identified as document number af-pnni-0055.002, all as known to those skilled in the art of communications networks.
In typical policy routing mechanisms, and as described in the Policy Routing Specification, Network Elements (“Ne”) or Resource Partitions (“Rp”) may be identified and advertised throughout the network topology for purposes of routing traffic through the network in question. For instance, a network element may be a link or the entirety of a trunk group, whereas a resource partition may be a bandwidth partition of such a trunk group. In forwarding a traffic stream, a policy based request for forwarding may be made, wherein the request may describe a forwarding constraint to either (i) prescribe the avoidance or requirement of one or more particular network elements or (ii) prescribe the requirement of one or more particular resource partitions. Such a policy based request may be communicated by way of the forwarding constraint, such as a policy constraint, being assigned to a connection and signaled during the establishment of same. A node which is initiating the establishment of the network path for a traffic stream will use the advertised network elements and resource partitions together with the signaled policy constraint to compute or otherwise establish a network path that satisfies the constraint in question.
Policy routing capabilities may be used in communications networks to provide varying services based on different network utilization strategies. For instance, policy routing may be deployed in the provisioning of Virtual Backbone Networks (“VBN”), in the selection or avoidance of network paths associated with a predetermined link quality, in the routing of connections utilizing multiple ordered policy constraints, in the specification and use of bare network resources for inter-network core networks, in bandwidth partitioning between SVC and SPVC connections, and in the dynamic allocation of network bandwidth among identifiable categories of connections. However, in such policy-based systems, it has not been known to provide a system and method for identifying suitable pre-computed paths for connections when they reach a node in such a network.